Lag fuse



Oct. 27, 1953 G, F, LA|NG 2,657,294

LAG FUSE Filed April 16, 1952 INVENTo.

Patented Oct. 27, 1953 UNITED LAG FUSE' Gordon? 1" Laing; Deiavan, Wis.; assignorito.Econ-L omy'fEusandfManufacturngfzC0:, Chicagmalll'.,V ravcolrp,oraztinnmf Illinois Application Aprill'l', 1952;;Serial No; 282,603*

loaclaims... (Cl..200-.123-) This-invention relates toffuses vof fth'eeduall element type; which'combineb'othinstantaneousfand lag fuse Aelements arranged in series.

It is directed in general'towardthetype'offuse shown' in my United StatesfPatentf No; 2,613,297, issued on October 7, 1952; and -in'an application madeof even datev herewith vin the-names ofGordon'Y F. Laing and Gustav R'ensner,-S`erial No. 282,601.

In Lboth of these fusev constructions, the-lag `elements' areactuated afterian interval of timel during which currentoverload less than lthat vamountrequired to `blow the instantaneousV fuses increasesthe resident heat of thelag-elements'up-tol the temperature required'to fuse the eutectic solder by which they are held in closed circuit position. The' actuation of' the-elements'from closedr to open circuit positionis'effected byia-.tension spring arrangedto pull the elementsfout of engagementonce the solder fuses to makethisfpossible.

In the present invention, theelag elementsr` are forced into open position by a pushing action exerted upon one of them by a spring-actuated insulating member which pushes a moving circuit-carrying part from closed circuit to open circuit position, and holds it there in a positive manner.

Fuses constructed in accordance herewith are characterized by their simplicity of construction and reduced number of parts, and have the advantage over other constructions in that there is always a member bridging the space between opposed lag elements which is either conductive or insulative, depending upon the closed or open condition of the circuit. i

Reference will now be made to the accompanying drawings, in which- Figure 1 is a plan view showing a fuse according to the present invention in closed circuit condition, with some of the parts in section;

Figure 2 is a mid-sectional elevation of the construction shown in Figure 1 and taken at substantially a S90-degree position from the latter view;

Figure 3 is a view corresponding to Figure 2, showing the parts in open circuit position.

Referring now more particularly to the drawings, there is provided the usual insulating fiber or plastic casing I0, which has terminal caps I2 and I4 disposed to close the opposite ends thereof. Diaphragms I6 and I8 divide the casing into three chambers, in the end ones of which are positioned links 20 and 22 which extend from the terminals I2 and I4 through the diaphragms. I6 and I8 into the central chamber, Where they connect with spacedmassived4 metallic vconductor members 24 and 26g respectively. lAs shown in Figures 2and 3, these members arev bored coaxiallyfat 28 and-'30; respectively, and in thecase of fthe-element 24'afcountersir`1k` 32f is provided in the end wall thereof in relationtoits'bore-2`8 Within the latterA there--is-connedan expansion spring 34, againstvwhich an insulative-bridging plunger 36 is disposed. In the opposing lmassive member 2'6, a metallic plungery 3`8 isfdisposed Ain its bore'3, which plunger has-a1 contact head-40. secured thereto,` which -is't adapted to seat within the countersink 32 of-theoppo'sing-'member- 214'.l

In' the closed circuit position, thev metallicv plungerv 38 is caused tobridge the space between the massiverrnembers 24and`f2'61to causefits contactv head 4i!V to engage in thecounter-sink; 32,' where it is heldby eutecticsolder 424- applied at several points as indicated. When the* metallic plunger 38l is thus positionedto' close the circuit,

the' insulative plunger'Sii-y is forced intol the'bOre' 2`8` against the resistance to'-compression of fthespring 34. Let it be assumedthat-current representing an overload of insufficient magnitude to cause the fuse links 20 and 22 to burn out is passed through the parts arranged as shown in Figures 1 and 2: the massive members 24 and 26 commence gradually to heat until a temperature is attained that is in excess of the melting point of the eutectic solder 42. The solder then melts to release the metallic plunger 38, which is caused to come into open circuit position by the action of the spring 34 against the insulative plunger 36. This latter pushes the metallic plunger into open circuit position, as shown in Figure 3, and holds it in that position in a positive manner.

It will be seen from the foregoing description that when the fuse is in closed circuit position, the metallic plunger 38 bridges the space between the massive metallic conductors 24 and 26, and when its parts are in open circuit position, as shown in Figure 3, the insulative plunger 36 bridges the space between these massive members; so that at first the insulative plunger is displaced by the metallic plunger, and then the metallic plunger is displaced by the insulative plunger.

The end chambers, in which the links 20 and 22 are accommodated, may be filled with quenching powder 23, as is well known to the art.

I claim:

1. Lag fuse construction comprising dual fuse elements of the instantaneous and delayed action types, said elements being in series, said delayed action type element including a pair of relatively massive conductors of heat and electricity arranged in spaced relation, a movable conductive bridge carried by one of said massive conductors, an insulative bridge carried by the other or said massive conductors, said conductive and insulative bridge means being mutually displaceable across the space between said massive conductors, means pushing said insulative bridge against said conductive bridge to urge the latter out of bridging relation across said space, and fusible means connecting said conductive bridge to at least one of said massive conductors resisting said displacement.

2. The invention of claim 1, said conductive and insulative bridge means being coaXially aligned with each other and with said massive conductors, each bridge being telescopically intertted with its respective conductor so as to alternately retract into and project outwardly therefrom.

3. The invention of claim 2, said pushing means being a compression spring disposed in the conductor within which said insulative bridge is retraotible, said spring bearing against said insulative bridge and forcing it to butt against said conductive bridge.

4. The invention of claim 1, said fusible means comprising eutectic solder having a predetermined metal point.

5. Fuse construction having instantaneous lag type fuses in series, said lag type fuse comprising a pair of massive metal members arranged in spaced relation, said members having bores coaxially arranged with respect to each other, a metallic plunger mounted in one of said bores and projecting therefrom across to the opposed member against which it is held by fusible material, and a compression spring and an insulative plunger mounted in the other of said bores, said insulative plunger being coniined against the tension of said spring in said other bore by said metallic plunger with the parts in closed circuit position.

6. The invention of claim 5, the outer end of said metallic plunger having a contact head thereon larger than either of the bores in said metal members and against which said insulative plunger butts, and a complementary contact bearing for the contact head on said metallic plunger confronting the latter on the opposed metal member.

7. The invention of claim 6, in which said complementary contact bearing is countersunk in said opposed member in relation to the bore thereof.

8. The invention of claim 5 further characterized by the fact that when the parts are in open circuit position the metallic plunger is pushed into retracted position within its massive metal member by said insulative plunger, which in turn is projected by the expansive force of the spring from the bore of its massive metal member within which it is confined when the parts are in closed circuit position, to displace the metallic plunger from bridging relation between said members, and to hold the metallic member positively in open circuit position.

9. The invention of claim 8, said lag type fuse parts being enclosed in the middle chamber of a three-compartment fuse casing, the end chambers of which accommodate the instantaneous type fuses in series therewith.

l0. The invention of claim 9, said casing having terminals thereon in which the instantaneous fuses terminate, the end chambers of said casing surrounding said instantaneous fuses being filled with quenching powder.

GORDON F. LAING.

References Cited in the le of this patent UNITED STATES PATENTS Number Name Date 2,286,518 Taylor June 16, 1942 2,296,627 Brown Sept. 22, 1942 

